1. Field of the Invention
The invention relates to a processing circuit, and more particularly to a processing circuit applied in an optical storage apparatus.
2. Description of the Related Art
In digital video disc (DVD) systems, data signals A, B, C, and D from light-receiving elements of a photo diode in a pickup head module comprise radio frequency (RF) signals and servo information. FIG. 1 shows a conventional processing circuit for processing data signals in a DVD system. Referring to FIG. 1, the RF signals of the data signals A, B, C, and D are transmitted to an RF front-end module, such as a summing module 10, through AC coupling paths to filter out their low-frequency components. Each AC coupling path comprises a large capacitor, such as capacitors C1 to C4. The RF signals of the data signals A, B, C, and D pass through capacitors C1 to C4 and corresponding input pins P1 to P4 to the summing module 10, respectively. The servo information of the data signals A, B, C, and D is transmitted to a servo front-end module, such as a servo-processing module 11, through DC coupling paths and corresponding input pins P5 to P8. In order to process the RF signals and the servo information simultaneously, the processing circuit must comprise a set of input pins for the AC coupling paths and a set of input pins for the DC coupling paths. Accordingly, as shown in FIG. 1, the processing circuit must provide at least eight input pins P1 to P8 for the data signals A, B, C, and D.
A processing circuit providing the same paths for RF signals and servo information of data signals A, B, C, and D, and requiring fewer input pins is desirable.